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18.04 doesn't use the interfaces file. Netplan is used now.
resolv.conf is managed by the resolvconf package, not manually since 12.04.
So, to start, we need to know which release you are using and which network devices are on your machine and where those devices are connected.
Let's start with these commands. Please show your work and please, please, please use "code tags" so the output lines up correctly.
Code:
sudo lshw -C network
ifconfig
route -n
I have no idea about debian versioning/releases and how that alters network configs. That isn't ubuntu.
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